When etching a polysilicon control electrode, the bottom corners of the polysilicon control electrode may be removed thereby undercutting or notching the control electrode. If the notching is uninhibited then the amount of undercutting is unknown and unpredictable, but, if controlled, the notching can be desirable. By predetermining the size of the notches in the control electrode, the gate length and the Miller capacitance of the polysilicon control electrode are desirably reduced.
As device dimensions shrink, there is a need to control the different threshold voltages (Vt) of the N-MOS and P-MOS devices. In addition, as the thickness of the gate dielectric decreases polysilicon depletion effects occur in the polysilicon control electrode. Substituting a metal material for polysilicon as a control electrode eliminates the polysilicon depletion effects. In addition, metal materials exist that have appropriate work function levels to set the desired threshold voltages for the NMOS and PMOS devices. Therefore, as the industry moves toward metal control electrodes, the benefits of undercutting a polysilicon control electrode are eliminated. Therefore, a need exists to be able to controllably decrease the gate length and miller capacitance of metal control electrodes.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention.